Method of treating liquors containing sulfurous acid or sulfites.



STATES PATEN onnio .WAL'IER H. DICKER SON, F MUSKEGON, MICHIGAN.

METHOD OF TREATING LIQUORS CONTAINING SULFUROUS ACID 0R SULFI'IES No Drawing.

Specification of Letters Patent.

Patented Apr. 22, 1913.

T 0 all whom it may concern:

Be it known that I, WALTER H. DIOKER- son, a citizen of the United States of America, residing at Muskegon, in the county of Muskegon and State of Michigan,

have invented certain new and useful Improvements in Methods of Treating Liquors Containing Sulfurous Acid or Sulfites, of

which the following is a specification.

My invention relates to the utilization of waste sulfite liquors resulting from the man ufa-cture of cellulose by the sulfite process,

furous' acid, such as calcium bisu lfite or cal- 1 cium sulfit-e. This acid is usually in excess:

so that some of it exists as free, unco'mbined acid, and also as gas in a state of solution.

I At higher temperatures such as those attained during the concentration of these liquors, the valuable organic constituents thereof decompose with considerable rapidity if the liquors contain any consider-' able amount of free acid. They decompose also with equal if not greater rapidity while alkaline. In order to prevent these decompositions as much as possible, it is advantageous to concentrate the liquors while they are weakly acid, in. which state there seems to be a minimum of decomposition. If,how-- ever, as is sometimes the case, any considerable proportion of sulfuric acid is formed during the evaporation of the liquors while acid, they undergo a marked decomposition which renders them unfit for many purposes. I have found that the liberation of free sulfuric acid in the liquors, even if in very small'proportions at first, seems to have an autocatalytic influence, in that it leads to the further formation of this or other acids increases accompanied by, correspondingly accelerated decompositions. Under these Application filed August 24, 1909. Serial No. 514,374.

conditions the liquors quickly become burned as it has been termed, andthereby lose much of their value for most pur poses. I have found that these deleterious decompositions during the treatment of waste sulfite li-qu-ors, due to the formation or liberation of sulfuric acid, may be prevented by having basic constituents in the solution to'c'ombine with and remove the sulfuric acid in the form of insoluble sulfates. Such basic constituents are barium or calcium, both of which combine with sulfuric acid and precipitate in insoluble form in acid solution. If a barium salt is relied upon to effect the removal of sulfuric acid as it is formed, it may be added in the form of the solid, barium carbonate, etc., or in solution in water, as for example a solution of barium chlorid. I have found, however, that the addition of extraneous compounds such as these, to precipitate sulfuric acid, is ,usually not necessary, but that the same effect is attained by allowing sufficient calcium salts to remain in weakly acid liquors during their evaporation. Waste sulfite liquors almost invariably contain "considerable amounts of calcium in solution as is well known. It has previously been customary to remove all of this by precipitation as an insoluble salt before the concentration of the liquor by evaporation. The only alternative to this practice, so far as Iam aware, has been the addition to the liquors of soluble alkaline compounds in excess in order to completely neutralize the free acid. Neither of these methods of procedure prevents the decompositionswhich it is the object of my invention to obviate. In the first instance, all the lime salts are removed; in the second instance, there may be an excess of lime in the liquors, but the decompositions which result in the formation of sulfuric acid, do not then occur, but rather others, which are, as I have said,equally deleterious. In order, therefore, to effect the concentration of waste sulfite liquors which contain calcium, I so treat them,-either after their discharge from the digester or after any subsequent treatment that might be found desirable, that they remain weakly acid and contain a sufiicient amount of dissolved calcium salts to combine with and precipitate all sulfuric acid which may be liberated or formed during the evaporation of the liquors. For example, if oxalic, phosphoric, sulfuric or other acids which form insoluble calcium compounds are added to the liquorsb'efo're their concentration, I make these additions only in such quantities as will leave in solution a suitable'slight proportion of unprecipitated calcium salts. The quantity ofcal cium which I thus retain in solution during evaporation can be quite small because the total amount of sulfuric acid formed during the concentration is very small, as long .as this'acid is removed practically as fast-as it is formed. It is only, as I have said, .{in the caseof its accumulation unhindered in the liquors that considerable quantities of it'are formed, and the aforesaid decomposition of the liquors occurs. In the presence of suitable basic constituentssuch as barium or calcium, these aforesaid decompositions and the formation of any considerable quantities of sulfuric acid does not occur, and the liquors may be safely concentrated either at normal pressures or in cacao, or further treated. Where it is desirable any calcium,

barium salts, etc., remaining-in solution, at the termination of concentration or further treatment, may be finally precipitated by the addition of suitable salts or acids with. which these basic constituents form insol-' uble compounds.

While this method of purifying liquors amounts, during the concentration or other treatment of the liquors.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

- 1. The method of preventing decomposition of waste sulfite liquors during concentration thereof which consists in precipitating" part of the basic constituents which form insoluble precipitates with sulfuric acid, and then concentrating the liquors whilethey are acid.

.2. The-method of preventing-decomposition of waste sulfite liquors during concentration thereof which consists in precipitating part of the .basic constituents which acid, and then concentrating the liquors while they are weakly acid. p,

3. The method of preventing decomposiform insoluble precipitates with sulfuric tion of products obtamed from waste sulfite liquors during concentration thereof which consists in precipitating constituents which form insoluble precipitates with'sulfuric acid, and then'concentrating the-liquors while they are acid.

t. The method of tion of productsobtamed from waste sulfite liquors during concentration thereof which reventing decomposipart [of the basic consists in precipitating art of the basic constituents which form lnsoluble precipitates with sulfuric acid, and then a-concentrating the liquors while -they are weakly 5. The method; decomposi-i tion of waste sulfite tration thereofv which consists in concentrating them while they are acid and contain soluble barium compounds.

iji'iors during concen 6." The method of'preventing decomposition of products obtained from waste sulfite liquors during concentrationthereof which consists in concentratin them; while they are acid and contain so uble barium compounds.

In testimony whereof I aiiix my signaturein presence of two witnesses.

WALTERZH. mcKERsoi t Witnesses: JEANNETTE STQRK,

A. L. KENT. 

